Question

For the following reaction at 298 K

2A + B → C

ΔH = 400 kJ mol-1 and ΔS = 0.2 kJ K-1 mol-1. At what temperature will the reaction become spontaneous? Considering ΔH and ΔS to be constant over the temperature range.

Answer 1

ΔG = ΔH - TΔS

For ΔG = 0, ΔH = TΔS or T = ΔH/ΔS

T = {400 kJ mol-1}/{2 kJ K-1 mol-1} = 200 K

Thus, reaction will be in a state of equilibrium at 200 K and will be spontaneous above this temperature.